In an interaction between sodium and chloride, which atom gains electrons? Which atom loses electrons?

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For the determining which atom loses an electron and which atom gains an electron, it is often very useful to consult the periodic table. From there, we are able to examine the chemical properties of an element; thus, determining their behavior in any chemical reactions. For this specific example between...

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For the determining which atom loses an electron and which atom gains an electron, it is often very useful to consult the periodic table. From there, we are able to examine the chemical properties of an element; thus, determining their behavior in any chemical reactions. For this specific example between sodium (Na) and chloride (Cl), Na is element number 11 (meaning that it has 11 protons and thus 11 electrons to make a neutral atom) while Cl is element 17 (with 17 protons and 17 electrons when neutral). Na is also known as an alkali metal, which are all the elements on the left-most column while Cl is in the halogen group. It is well known that alkali metals and halogens react very well together to form an ionic interaction, such as NaCl, where one element donates an electron to become positive and another accepts that electron to be negative, resulting in a positive-negative charge interaction.

To determine which atom would lose an electron and which would accept one, we must focus on the amount of valence electrons on that atom (in other words, the amount of electrons in their outermost shell). Atoms like to attain the most stable energy level possible by having the maximum amount of electrons possible in its outermost shell but sometimes they can only do so through chemical reaction with other atoms. For the alkali metals, there is one electron in their outermost shell while halogens have seven. The full shell consists of eight electrons. As a result, it is much easier for halogens to obtain just one electron to complete the octet and for the alkali metal to lose that one remaining electron in its outermost shell so that their next outermost shell contains a full octet. This is what happens with Na and Cl. Na loses an electron to obtain a full octet while Cl obtains an electron to obtain a full octet. This creates Na+ and Cl-, which form an ionic interaction to become NaCl (neutral because + and - cancel each other out) commonly known as table salt.  

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